Compressor lubrication apparatus for closed reversible cycle ice-making systems

ABSTRACT

Apparatus for concurrently circulating a refrigerant and a refrigerant oil through a closed reversible cycle ice-making system having interconnected compressor, condenser and evaporator components and in a manner which provides efficient heat exchange, capacity and compressor lubrication. The invention is characterized by a combination of three interdependent features, namely, (1) During the ice-forming phase, an emulsion of a refrigerant and a refrigerant oil is caused to flow through the evaporator chamber at sufficient velocity and turbulence to prevent substantial adherence of the oil to the chamber side walls and to produce substantially uniform freezing temperatures on the wall surfaces; (2) During the alternate defrosting phase and when the emulsion has separated into hot gaseous refrigerant and refrigerant oil, the gaseous refrigerant is caused to flow through the chamber at sufficient velocity to suspend the oil and sweep it from the chamber walls, and (3) During both of said phases, a positive pressure drop across the evaporator chamber is maintained within the range of 0 lbs./sq. in. to 2 lbs./sq. in. to thereby create a balanced efficiency between oil circulation and heat exchanger on one hand, and the capacity of the system on the other.

United States Patent 1 Gordon 1 Nov. 6, 1973 COMPRESSOR LUBRICATIONAPPARATUS FOR CLOSED REVERSIBLE CYCLE ICE-MAKING SYSTEMS [76] Inventor:Robert W. Gordon, PO. Box 606,

Longwood, Fla. 32750 [22] Filed: May 26, 1972 [21] Appl. No.: 257,299

Primary Examiner-William E. Wayner Attorney-Robert Brown, Jr.

[57] ABSTRACT Apparatus for concurrently circulating a refrigerant and arefrigerant oil through a closed reversible cycle ice-making systemhaving interconnected compressor, condenser and evaporator componentsand in a manner which provides efficient heat exchange, capacity andcompressor lubrication. The: invention is characterized by a combinationof three interdependent features, namely, (1) During the ice-formingphase, an emulsion of a refrigerant and a refrigerant oil is caused toflow through the evaporator chamber at sufficient velocity andturbulence to prevent substantial adherence of the oil to the chamberside walls and to produce substantially uniform freezing temperatures onthe wall surfaces; (2) During the alternate defrosting phase and whenthe emulsion has separated into hot gaseous refrigerant and refrigerantoil, the gaseous refrigerant is caused to flow through the chamber atsufficient velocity to suspend the oil and sweep it from the chamberwalls, and (3) During both of said phases, a positive pressure dropacross the evaporator chamber is maintained within the range of 0lbs/sq. in. to 2 lbs/sq. in. to thereby create a balanced efficiencybetween oil circulation and heat exchanger on one hand, and the capacityof the system on the other.

1 Claim, 3 Drawing Figures AAA.

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COMPRESSOR LUBRICATION APPARATUS FOR CLOSED REVERSIBLE CYCLE ICE-MAKINGSYSTEMS This invention relates to lubrication and more particularly to aclosed reversible cycle ice-making system having improved heat exchange,oil return to the compressor, and capacity operation.

The present invention is adapted to be associated with conventionalautomatic ice-making systems such as disclosed in US. Pat. No. 3,146,610and which are provided with a compressor, a condenser and an evaporator.In such systems, the evaporator usually comprises upright concentricallyspaced tubular members between which a fluid media consisting of anemulsion of a refrigerant and a refrigerant oil flows in condensedliquefied form during the ice-forming phase, and between which therefrigerant in a hot gaseous form and the separated refrigerant oil flowduring the iceharvesting or defrosting phase. Heretofore, therefrigerant and oil have been conducted through the evaporator chamberwithout due regard to the basic principles of hydraulic flow and,consequently, highly localized eddy and counteracting currents haveproduced wide variations in heat exchange, excessive pressure drops andoil accumulation in the evaporator chamber resulting in defectivecompressor lubrication, and also a reduction in the overall capacity ofthe system (See US. Pat. No. 3,327,494). In the latter patent, the lackof uniformity of heat exchange inthe refrigerant chamher was of primaryconcern, and especially with respect to the excess heat exchange and iceformation at the bottom of the evaporator coupled with a deficiency atthe top. The solution proposed in this patent, however, was inadequatebecause the oppositely acting refrigerantjets promoted more turbulenceat the bottom of the chamber without increasing the turbulence in theupper portions thereof, resulting in an excess ice accumulation at thebottom as well as a less efficient oil return to the compressor.

It is therefore an object of this invention to create a concurrent flowof refrigerant and refrigerant oil through the evaporator of anice-making system of the class described, which flow will producesubstantially uniform freezing temperature throughout the evaporatorchamber during the ice-forming phase, and will further produce in thechamber a suspension of the oil in the gaseous refrigerant during thedefrosting phase to thereby prevent the oil from becoming logged in theevaporator.

It is another object of this invention to provide a system of the classdescribed having a balanced efficiency as between oil circulation andice producing heat exchange on one hand, and the overall capacity of thesystem on the other. In this connection, it should be noted that theconditions favoring uniform freezing temperature and the efficient oilsuspension in the evaporator chamber are opposed to those favoring ahigh capacity of the system. High refrigerant velocity and uniformturbulence tend to effect a more efficient heat transfer, and also tendsto keep the oil insuspension during the defrosting phase. Nevertheless,the high velocity tends to produce an undesirable pressure drop which,in turn, promotes inefficient operation of the system. Therefore, acompromise condition is adopted which permits the opposing conditions toserve their respective goals. Extensive research has proven that apressure drop in the evaporator chamber ranging between 0 lbs/sq. in.and 2 lbs/sq. in. are critical limits satisfying the opposingconditions. By confining the pressure drop to this range, neither of theheat exchange, oil circulation, nor the system capacity factors will beincreased or diminished to a serious detriment of the others.

Some of the objects of invention having been stated, other objects willappear as the description proceeds when taken in connection with theaccompanying drawings, in which,

FIG. 1 is an elevational view of an evaporator according to theinvention with certain portions thereof broken away and other portionsin section, and further showing schematically an associatedrefrigerating system for making ice;

FIG. 2 is a sectional plan view of the top portion of the evaporator andtaken along line 2-2 in FIG. 1; and

FIG. 3 is a sectional plan view taken along line 3-3 in FIG. 1.

Referring more particularly to the drawings, the numeral 10 indicatesbroadly an evaporator comprising an upright outer tubular member 11, asubstantially concentric inner tubular member 12, and an annularrefrigerant chamber 14 separating the two members said chamber beingsubstantially free of any fluid guide means. Chamber 14 is sealed at itstop by means of a plate 15 and at its bottom by an outwardly flared endor skirt of inner tubular member 12.

Surfaces lla and 12b of members 11 and 12 respectively are sprayed withwater from spray heads 16 and 17 concurrently with the flow of arefrigerant through chamber 14 thereby causing ice to form on thesesurfaces during the freezing phase of an operating cycle. The freezingphase is followed by a defrosting or iceharvesting phase during whichhot gaseous refrigerant is caused toflow through chamber 14 to releasethe ice from surfaces 11a and 12b. In order to properly lubricate thesystem, and especially the compressor 27 thereof, a suitable refrigerantoil is added to the refrigerant.

The refrigerant and refrigerant oil are introduced into chamber 14 bymeans of an injector tube 18, which tube extends downwardly throughplate 15 into and near the bottom of the chamber. The tube has anarcuate laterally extending lower end portion 18a provided with orifice18b for directing the refrigerant and oil substantially tangentially ofthe chamber centerline 14a and against the concave inner wall surface 11b of tubular member 11, said refrigerant and oil then deflecting fromsurface 11b to thereafter flow circumferentially and unidirectionallyabout the centerline 14a as it swirls in a cyclonic manner upwardlytoward outlet 20 at the top of the chamber.

Although the refrigerant and oil swirl at a maximum velocity at thepoint of discharge 18b andwith some decrease in velocity as it travelsupwardly, the velocity is always sufficient to produce substantiallyuniform freezing temperature on the ice-forming surfaces of the chamber.In fact, it is necessary to have some decrease in velocity in order toprevent an undesirable pressure drop in the evaporator. As a result ofthe unidirectional swirling action and turbulence, a uniform thicknessof ice is produced upon the surfaces lla and 12b. Moreover, thisvelocity and turbulence is especially desirable during the defrostingcycle to keep the oil suspended in the hot gaseous refrigerant and keepit moving through the evaporator and back to the compressor 27.

It is important to note that the injector tube is employed forcirculating fluids into chamber 14 during both the freezing andharvesting phases of operation. The upper end of tube 18 communicateswith refrigerant supply circuit through a line 23 and a hot gaseousdefrost circuit through line 25a. The refrigerant supply is controlledby an external equalized expansion valve 22 during the ice-formingphase, and the hot gaseous refrierant supply is controlled by gas valve24, said valves being operated alternately in a conventional mannerduring the freezing and harvesting phases. By suitably altering theconfiguration of tube portion 18a and/or the sizes of openings 18b andand by creating a substantially uniformly distributed helicalunidirectional flow from the bottom to the top of chamber 14, thepositive pressure drop across the evaporator chamber (i.e. betweenorifice 18b and outlet 20) may be limited to the critical value of notmore than 2 lbs./sq. in.

The above-described system may comprise the compressor 27, a condenser28, a heat exchanger 29, and a surge tank 30. Members 27 through 30 areconnected as follows: high pressure discharge line 31 connectscompressor 27 to line line 25 connects line 31 to the upper portion ofcondenser 28; line 32 connects the lower portion of the condenser to thelower portion of heat exchanger 29; line 33 connects the upper portionof the heat exchanger to external equalized expansion valve 22, saidconnections being located on the pressure side of the compressor. On thesuction side of the compressor, line 36 leads through heat exchanger 29and into the upper portion of surge tank and another line leads from theupper portion of said tank to the evaporator outlet 20. A suitablecoolant such as water enters condenser coil 39 as at 40 and leaves thecoil as at 41.

During the freezing phase, valve 24 is closed, at which time thecompressed hot gaseous refrigerant and refrigerant oil flow fromcompressor 27, through lines 31 and 25 and condenser 28 to extract heattherefrom and thereby form a liquid emulsion of the refrigerant and theoil. From the condenser 28, the emulsion continues to travel through theheat exchanger 29, line 33, expansion valve 22, line 23, injector tube18, chamber 14, surge tank 30, suction line 36, and back to thecompressor. While the emulsion is in chamber 14, it separates intorefrigerant gas and oil components, at which time the oil tends tosettle rather than travel with the gaseous component.

During the ice-harvesting phase, the valve 24 is opened to permit thehot gaseous refrigerant and the oil to flow from the compressor 27,through line 31, line 25a, valve 24, injector tube 18, chamber 14, line35, surge tank 30, line 36, and back to the compressor. Unlesssufficient velocity of the hot gaseous refrigerant is maintained to keepthe oil in suspension, the abovementioned tendency for theoil to settlewill occur and thus restrict oil circulation and lubrication of thecomponent parts of the system. 1 1

The above-described ice-producing and lubricating apparatus may beoperated automatically in a wellknown manner by circuitry such as shownin the aforementioned US. Pat. No. 3,146,610.

The following basic facts emphasize the importance of the constructionand method steps employed to properly lubricate the ice-making system:

In a mechanical refrigeration system, the return of the oil to thecompressor is of critical importance. The oil in the refrigerant is theonly means of lubrication of the compressor and the lack of it is themost common cause of compressor failure. Hence, an adequate amount ofoil must always circulate with the refrigerant.

Liquid refrigerant is miscible with oil. The refrigerant gas and oil,however, do not mix readily and the oil can be properly circulatedthrough the system only if the design is such that the velocity of therefrigerant in its gaseous state is great enough to sweep the oil along.If the velocities are not sufficiently high, the oil will tend to lie onthe bottom of the refrigerant tubing and the evaporator and cling to theevaporator walls, thereby causing oil clogging and decreasing the heattransfer capability of the evaporator due to the insulating effect ofthe oil. As more oil is trapped in the system, a shortage could developin the compressor causing bearing failure.

As the evaporating temperatures are lowered, the problem becomes morecritical since the viscosity of the oil increases with the decrease intemperature. For this reason, proper velocity control and turbulence areessential for satisfactory oil return. Several factors combine to makeoil return most critical at low evaporating temperatures. As the suctionpressure decreases and the refrigerant vapor becomes less dense, themore difficult it becomes to sweep the oil along. At the same time, asthe suction pressure falls the compressor ratio increases and as aresult the compressor capacity decreases. Refrigerant oil at 0F. takeson the consistency of molasses, but as long as it is mixed withsufficient liquid refrigerant, it flows freely. As the percent of theoil in the mixture increases, the viscosity increases requiring greatervelocity and turbulence to move it along. At low temperature, all thesefactors start to converge and tend to create a critical condition inwhich the density of the gas decreases, the mass velocity flowdecreases, and as a result, more oil starts to accumulate in theevaporator.

As the oil and refrigerant mixture becomes more viscuous, at some pointthe oil starts logging in the evaporator rather than returning to thecompressor, resulting in wide variations in the compressor crankcase oillevel. This condition will not occur if sufficient velocity andturbulence is created in the evaporator. The present evaporator design,when operated in accordance with the herein disclosed method, createssufficient uniform velocity and turbulence to overcome this problem evenat extremely low temperatures.

Although turbulence is desired and in fact essential to effect a moreefficient heat transfer, it has not been satisfactorily attainedheretofore in conjunction with adequate compressor lubrication, insofaras I am aware. As the pressure leaving the evaporator at outlet 20 isdecreased, the specific volume of gas returning to the compressorincreases and the weight of the refrigerant pumped by the compressordecreases. Therefore, the pressure drop in the evaporator causes adecrease in system capacity.

it is important to note that the refrigerant oil tends to becomeunsuspended and accumulate within the evaporator 10 during the freezingphase as well as during the defrosting phase. During the freezing phase,the liquid enters the evaporator at 18b and immediately expands into agas state. Therefore, the oil tends to precipitate out of the gas andcling to the walls of chamber 14, especially in the uppermost portionsof the chamber. Hence, the necessity of limiting the pressure drop tothe critical maximum continues during the freezing phase.

The goals of low pressure and high velocity are directly opposed;consequently, the evaporator design must be a compromise. In the presentdesign, a uniform turbulence is created which keeps the oil swept fromthe walls of the evaporator during both phases, increases the heattransfer throughout the evaporator, and causes a pressure drop of notmore than 2 p.s.i. in the evaporator. This lack of pressure beyond thislimit will cause the compressor to draw less power in its operations,resulting in more efficiency for less operating cost.

Briefly stated, the present method and apparatus creates a more uniformvelocity and turbulence in the evaporator which, in turn, creates a moreuniform heat transfer throughout the length of the evaporator andcontributes to more efficient ice production; creates better oil returnto the compressor, reducing the possibility of compressor failure, andreduces the evaporator drop to not more than 2 p.s.i., resulting in amore efficient system.

I claim:

1. Compressor lubrication apparatus for a closed re- 6 versible cycleice-making system comprising: a con denser; a compressor; an evaporator,said evaporator including a pair of spaced upright substantiallyconcentric members forming a sealed annular chamber therebetween, saidchamber being substantially free of any fluid guide means between theinner opposed walls thereof, the respective areas of said members remotefrom the chamber defining ice-forming surfaces; means including saidcompressor for circulating during the freezing phase a refrigerant-oilmedia under high pressure an upwardly and unidirectionally in a helicalpath extending from the bottom to the upper portion of said chamber; andmeans including said compressor for circulating during the alternatedefrosting phase the separated refrigerant and oil of said media underrelatively low pressure and upwardly and unidirectionally in saidhelical path, said last-named means consisting of an inlet nozzlepositioned horizontally and tangentially at the bottom portion of thechamber and adapted to direct the media into one end of said helicalpath, and an outlet at the upper portion of the chamber communicatingwith the other end of said path, whereby the velocity and turbulence ofthe media will produce asubstantially uniform heat exchange in thechamber while preventing a pressure drop across the chamber as a resultof the accumulation of unsuspended oil therein.

1. Compressor lubrication apparatus for a closed reversible cycleice-making system comprising: a condenser; a compressor; an evaporator,said evaporator including a pair of spaced upright substantiallyconcentric members forming a sealed annular chamber therebetween, saidchamber being substantially free of any fluid guide means between theinner opposed walls thereof, the respective areas of said members remotefrom the chamber defining ice-forming surfaces; means including saidcompressor for circulating during the freezing phase a refrigerant-oilmedia under high pressure an upwardly and unidirectionally in a helicalpath extending from the bottom to the upper portion of said chamber; andmeans including said compressor for circulating during the alternatedefrosting phase the separated refrigerant and oil of said media underrelatively low pressure and upwardly and unidirectionally in saidhelical path, said last-named means consisting of an inlet nozzlepositioned horizontally and tangentially at the bottom portion of thechamber and adapted to direct the media into one end of said helicalpath, and an outlet at the upper portion of the chamber communicatingwith the other end of said path, whereby the velocity and turbulence ofthe media will produce a substantially uniform heat exchange in thechamber while preventing a pressure drop across the chamber as a resultof the accumulation of unsuspended oil therein.